Astronomers in Italy and Germany have used some of the oldest stars in the Milky Way to estimate the true age of the universe and finally solve the long-standing Hubble tension mystery.
Researchers from the University of Bologna in Italy and the Leibniz Institute for Astrophysics Potsdam (AIP) used precise stellar data to determine that the Milky Way, including the solar system, may be 13.6 billion years old.
Although this age contradicts the young universe suggested by Cepheid and supernova measurements, it is consistent with the older age estimated from the cosmic microwave background. It adds a new perspective to the Hubble tension debate.
“This project perfectly demonstrates how combining expertise from different fields can open new windows for solving fundamental problems,” said Elena Tomasetti, a PhD student at the University of Bologna and lead author of the study.
a new approach to the universe
The Hubble constant, a measure of how fast the universe is expanding today, is one of the most controversial issues in modern cosmology. Although estimated to be around 68 kilometers per megaparsec (km/s/Mpc), its exact value remains controversial.
Meanwhile, different measurement methods have produced conflicting results over the years. Observations based on nearby cosmic objects such as Cepheid variables and supernovae indicate that it is expanding faster. This corresponds to a young universe of about 13 billion years.
In contrast, measurements based on the cosmic microwave background, the faint afterglow of the Big Bang, suggest that expansion is slower and that the universe is slightly older, about 14 billion years.
Photo credit: Elena Tomasetti
“Measuring the ages of stars is a complex challenge in itself, but we now live in an era where the amount and quality of available data allow us to achieve unprecedented precision and obtain statistically significant results for the first time,” Tomasetti said.
To address this challenge, the team focused on the ages of the oldest stars in the Milky Way. Since the universe cannot be younger than the stars it contains, accurately measuring the ages of the oldest stars in the Milky Way can provide a reliable lower limit on the age of the universe.
Clues from ancient stars
For this project, the team took advantage of an existing stellar age catalog developed by AIP, which contains age estimates for more than 200,000 stars in the Milky Way. Data from the European Space Agency’s Gaia mission provides precise measurements of stellar distances and spectra.
This information allows scientists to determine the properties of stars with unprecedented precision. Using this data set, the team selected carefully scrutinized samples of the oldest stars with the most reliable age measurements.
They prioritize quality over quantity and filter out objects that could skew results. The final sample included approximately 100 ancient stars, whose ages were determined using the StarHorse computational framework.
AIP senior scientist Dr. Cristina Chiappini noted that the Gaia mission effectively turns the Milky Way into a near-field cosmology laboratory. “We can now estimate stellar ages with unprecedented precision,” Chiappini said.
“The next breakthrough will be accuracy, anchoring the galactic timeline with greater certainty,” she concluded in the press release. “HAYDN’s mission concept, with the participation of AIP, aims to take a decisive step forward.”
Future data releases from Gaia are expected to further improve age estimates and could refine measurements of the age of the universe and the Hubble constant.
The research has been published in the journal Astronomy and Astrophysics.